A gas turbine absorbs an atmosphere. Under a normal condition, an atmosphere contains lithometeors having particle diameter of 1 μm to 10 μm Disclosure of Invention. When such a lithometeor is absorbed in a gas turbine and adheres on a rotor blade in an air compressing device, a fluid resistance increases; thus, an output loss increases. As a result, there is a problem in that an electricity generation output decreases. In order to prevent such a problem, as shown in FIG. 10, a dust collecting device 1 (filter unit) is disposed in the air intake device in the gas turbine so as to remove the lithometeors for cleaning the absorbed air in the air compressing device.
A dust collecting device 1 shown in FIG. 10 having two stages comprises a housing 2 which is connected to the air compressing device (not shown in the drawing), a coarse filter 3 (pre-filter) which is disposed in uppermost stream in the housing 2, and a middle-efficiency filter 4 for removing mainly lithometeors having a particle diameter which is finer than the coarse filter 3.
By the above dust collecting device 1, approximately 30% of lithometeors having approximately 1 μm of particle diameter in the absorbed air which absorbed in the housing 2 are removed by passing through the coarse filter 3. Furthermore, approximately 70% of lithometeors having approximately 1 μm of particle diameter in the absorbed air are removed by passing through the middle-efficiency filter 4.
As explained above, from an energy generating efficiency point of view, in a gas turbine, it is preferable that lithometeors in an atmosphere which are absorbed should be minimized. Therefore, more efficiency in collecting and removing the dusts is required. In such a case, a dust collecting device 5 having three stage structure is used as shown in FIG. 11.
In addition to the coarse filter 3 and the middle efficiency filter 4 which form the dust collecting device 1, the dust collecting device 5 further comprises a high efficiency filter 7 (High Efficiency Particulate Air Filter, hereinafter called as a HEPA filter) in a downstream. The HEPA filter 7 can remove 99.97% or more of lithometeors having approximately 0.3 μm of particle diameter. It is possible to remove approximately all of lithometeors contained in an atmosphere by these filters 3, 4, and 7.
As explained above, although the dust collecting device 5 having three stage structure can achieve high dust collecting efficiency, a size of the dust collecting device becomes larger so as to dispose the HEPA filter therein. If the device becomes larger, a space for installation needs to be larger; thus, the installation of the device often becomes difficult. According to such a condition, it has been requested that the size of the device be decreased.
For such an object for making a small device, there has been developed a layered filter device having a middle efficiency filter and a HEPA filter unitarily. An example for a conventional layered filter device is shown in FIG. 12. A layered filter device 8 shown in FIG. 12 comprises a frame 8a having a rectangular shape, a layered filter 8b which is folded to be contained in the frame 8a, and a partition 8c which separates wall sections which neighbor each other in the layered filter 8b. A layered filter 8b is formed by simply layering and folding the middle efficiency filter 8b1 and the HEPA filter 8b2. The middle efficiency filter 8b1 and the HEPA filter 8b2 are disposed so as to be separated each other.
In such a conventional layered filter device 8, size of the device becomes smaller by forming the middle efficiency filter 8b1 and the HEPA filter 8b2 unitarily. However, from a dust collecting efficiency point of view, there is a case in which a required performance cannot be realized necessarily only by folding the layered filter 8b so as to increase a filtering area. That is, dust-collecting capacity is small in such a folded layered filter; thus, a product life in such a filter becomes short; therefore, it is necessary to exchange the filters in a short period.
Generally, in a gas turbine, it is preferable that it is possible to operate a gas turbine continuously for one year (8,760 hours of operational time) without exchanging the filter. However, a product life in the above conventional layered filter device 8 has been so short that the device could be operated only for half a year.
In order to realize a longer product life in a filter in the above layered filter device 8, one idea is to increase the filtering area by forming fine gaps on the layered filter device 8. However, as explained above, the layered filter 8b is formed by attaching and folding the middle-efficiency filter 8b1 and the HEPA filter 8b2 simply such that the middle-efficiency filter 8b1 and the HEPA filter 8b2 are disposed so as to be separated each other. Therefore, it has not been possible to form fine gaps while maintaining the condition under which the middle-efficiency filter 8b1 and the HEPA filter 8b2 should not be removed from each other.
The present invention was made in consideration of the above problems. An object of the present invention is to provide a dust collecting filter, a dust collecting device, and an air intake device for a gas turbine which are provided with a layered filter medium which can increase the filtering area so as to maintain a high dust-collecting efficiency for a longer hour under a small size condition.